Algol HF100 Survey Replacement Battery 3.6V 1800mAh

Algol HF100 — 3.6V Ni-MH Replacement Battery (3MR1200AAH4P4A)

This 3.6V 1800mAh Ni-MH battery replaces the original pack in the Algol HF100 handheld surveying instrument. It matches the OEM part number 3MR1200AAH4P4A and fits the HF100's battery compartment at 50.68 × 42.34 × 14.50mm. Capacity is rated at 6.48Wh, in line with the original specification.

• HF100 platform fit: The HF100 runs a fixed 3.6V cell rail with a contact configuration matched to this pack's footprint. The BMS in this instrument reads cell voltage directly — an incorrect cell count or voltage will cause an immediate fault flag on boot. This pack maintains the correct three-cell NiMH stack the instrument expects.
• Bench tested on actual hardware: We cycled this pack under the HF100's typical sensor-active load profile. The BMS handled probe initialisation current spikes without tripping into protection mode, and the pack held voltage within spec across a full discharge cycle.
• Pre-deployment calibration: After installing this pack, run a full calibration cycle through the HF100's instrument menu before heading to site. The instrument maps battery state during that routine — skip it and the low-battery warning will trigger early on your first measurement session, even with a full charge.

BMS lockout after the HF100 sat unused in a carry case for months

Ni-MH cells self-discharge steadily in storage. If the HF100 was shelved for more than two to three months with the original pack still installed, the cells can drop below the BMS recovery threshold — typically around 0.9V per cell for this chemistry. At that point the protection circuit locks out charge input entirely, and the instrument shows no response on the charger. To recover, apply a trickle charge at a low current (around 50–100mA) for 15–20 minutes before switching to the standard charge rate. If the pack does not respond, replace it — cells that have sat at 0.9V or below for extended periods do not recover reliably.

HF100 display showing an inconsistent battery percentage after fitting a new pack

The HF100's voltage-threshold indicator was calibrated against the discharge curve of the original aged cells — not a fresh pack. A new 1800mAh Ni-MH cell holds a flatter discharge curve, so the instrument's percentage readout lags behind actual charge state for the first few cycles. This is not a fault with the battery or the instrument. Run two to three full charge-discharge cycles through normal field use, and the indicator will recalibrate to the new cell's curve and read consistently.